We report a new 'spark erosion' technique for producing high-quality thermoelectric nanoparticles at a remarkably high rate and with enhanced thermoelectric properties. The technique was utilized to synthesize p-type Bi(0.5)Sb(1.5)Te(3) nanoparticles with a production rate as high as 135 g h(-1), using a relatively small laboratory apparatus and low energy consumption. The compacted nanocomposite samples made from these nanoparticles exhibit a well-defined, 20-50 nm size nanograin microstructure, and show an enhanced figure of merit, ZT, of 1.36 at 360 K. Such a technique is essential for providing inexpensive, oxidation-free nanoparticles which are required for the fabrication of high performance thermoelectric devices for power generation from waste heat, and for refrigeration.

We report on the properties of low-temperature phase (LTP)-MnBi particles produced by the rapid-quenching technique of spark-erosion. The as-prepared powder consists of amorphous, crystalline, and superparamagnetic particles, mostly as porous aggregates. The major fraction of the powder consists of 20–30 nm particles. A short anneal crystallizes the amorphous particles producing a high moment, >90% of theoretical MS, albeit with HC of a few kOe. If lightly milled, the agglomerates are broken up to yield HC of 1 T. These findings are supported by the x-ray diffraction pattern showing broadened peaks of the predominant LTP-MnBi phase. The combination of spark erosion, milling, and annealing has produced randomly oriented particles with (BH)MAX ∼ 3.0 MGOe. The particles are expected to show record energy product when aligned along their crystallographic easy axes.

Summary The concept of energy‐sampling stabilization is used to develop a mean‐strain quadratic 10‐node tetrahedral element for the solution of geometrically nonlinear solid mechanics problems. The development parallels recent developments of a “composite” uniform‐strain 10‐node tetrahedron for applications to linear elasticity and nonlinear deformation. The technique relies on stabilization by energy sampling with a mean‐strain quadrature and proposes to choose the stabilization parameters as a quasi‐optimal solution to a set of linear elastic benchmark problems. The accuracy and convergence characteristics of the present formulation are tested on linear and nonlinear benchmarks and compare favorably with the capabilities of other mean‐strain and high‐performance tetrahedral and hexahedral elements for solids, thin‐walled structures (shells), and nearly incompressible structures.

Metallic foams of ferromagnetic Ni-Mn-Ga Heusler alloy show an 8.7% magnetic field induced strain (MFIS) [1]. The large MFIS in foams are orders of magnitude higher compared to bulk polycrystalline Ni-Mn-Ga, revealing that porosity is responsible for the increase in MFIS. Additive manufacturing (AM) techniques such as powder-bed binder-jet technique, known as 3D printing, are suitable for producing near-net shaped parts with controlled porosity. AM is a relatively new method of engineering that produces near-net shape components, one layer at a time, based on a computer aided design (CAD). The purpose of this work is to manufacture functional near-net shape parts with predetermined porosity from pre-alloyed ferromagnetic Ni-Mn-Ga powders using powder-bed binder-jet 3D printing technique. 3DP resemble ink-jet printing, but with multiple passes to build the materials upwards into a threedimensional form. This method has been proved successful in additive manufacturing near-net shape parts made from pre-alloyed Ti-Ni-Hf powders [2]. Bulk Ti-Ni-Hf alloy is a known high-temperature shape memory alloy [3].Pre-alloyed spherical Ni-Mn-Ga powders used in this experiment have been produced by spark-erosion in argon and nitrogen dielectrics. Recommended printing parameters (layer thickness, binder saturation, spread speed) for metallic powders by 3D printer manufacturer (ExOne, North Huntington, PA) did not prove successful for Ni-Mn-Ga spark-eroded powders. Binder saturation is a major parameter in the printing process. Binder saturation level affects both the breaking strength, as well as the dimensional tolerance of the green printed part. Insufficient binder reduces the mechanical strength of the green part, which can affect the integrity of the part when removed from the printer, or manipulated in between the printer and curing oven. A higher binder saturation level can produce lateral spreading, therefore affecting the dimension and surface quality of the final product. A water-based binder, provided by ExOne, was used in the experiment. In order to find the optimum binder saturation for Ni-Mn-Ga powders, a method similar to the bench top test was used [4]. Cured samples impregnated with various amounts of binder were investigated using SEM, Figure 1. The 2.0 µL of binder impregnation seemed to provide an adequate amount of binder for the printing process. Using the optimized printing parameters, green Ni-Mn-Ga parts were obtained. Figure 2(a) shows a green part after binder curing at 463K for 4 h.The green Ni-Mn-Ga parts were sintered in controlled atmosphere at various temperatures for varying periods of time. Figure 2(b) shows a low magnification SEM micrograph of the sintered part. It can be easily notice, voids are visible and the part is porous. The martensitic transformation behavior of sintered Ni-Mn-Ga parts has been analyzed by XRD, DSC, SEM, FIB, and TEM. The XRD investigation shows that the printed material displays Ni 2 MnGa Heusler phase. Based on the DSC investigation the sintered material shows revers...

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